This paper examines constitutions as constraining mechanisms. The first section reviews the common view that constitutions are mechanisms for constraining political enemies or unsympathetic constitutional decision makers. The second section examines invalidation, neglect, circumvention and capture, the strategies unsympathetic constitutional decision makers may employ when seeking to frustrate efforts to constrain them constitutionally. The last section explores the limited capacity constitutional reformers have to prevent or inhibit invalidation, neglect, circumvention and capture. Constitutionally constraining unsympathetic decision makers is at best a reasonable strategy for achieving a particular constitutional result, such as establishing the date on which a president takes office. Constitutional reformers seeking fundamental regime change, must employ other strategies for making their constitutional vision the official law of the land.